Apple iPhone Tech Talk London 2009: Overview

Apparently I can blog about this year’s Apple iPhone Tech Talk World Tour, so here’s my notes.

This was a much larger event than last year — and I wasn’t the only person surprised by how many developers turned up. Since the registration process involved entering an iTunes URL, most of the people present must have written an app and got it into the store. However, the gender balance was even worse some recent developer events I’ve attended — it looked like there were more women on the Apple team than in the whole audience…

The kickoff session was a quick rundown of where iPhone development has got to since it launched only 15 months ago (seems like longer, possibly because the jailbreakers got there a fair amount earlier…), and the rest of the day was spent going into details (I'll cover the sessions I attended in later posts). I really hope the Apple guys put their presentations up soon, as there was a lot of great detail that I couldn’t type fast enough to get down :-)

stats

• only 15 months since App Store launched (though an extra year of iPhone)
  • 2 Billion apps, means 180,000 apps an hour…
  • 100,000 apps in app store
• more than 50 million devices
• 81 countries
• 125,000 registered developers
  • so at least 25,000 who paid money but haven’t put anything in the store yet!

timeline

• jun 08: seeding SDK & emulator to all devs
• jul 08: app store live
• sep 08: customer reviews only by purchasers & versions
• oct 08: crash reporter & logs
• mar 09: developer discussion forum (still beta), more customer service agents
• jun 09: quick reference guides
• jul 09: news & announcements + better developer support
• sep 09: new app store categories (genius, essentials), top grossing lists, app store resource centre
• oct 09: in-app purchase available to free apps

the best apps are…

• simple or sophisticated (hiding complexity)
• lightweight
• intuitive
• small pieces loosely joined
  • lots of separate features
  • what about feature interaction? is that going to be a problem?

iPhone users have changed

• not necessarily technically savvy
• bringing technology into new places

specific examples of innovative apps

• each app has 5-7 seconds to sell itself to the user
  • it helps to have a memorable aspect
• use the latest technologies
• go the extra mile

• keep it fresh

• urbanspoon

  • shake to randomly choose a restaurant in the style of a fruit machine
• peaks
  • Augmented Reality (AR) for mountains
• car finder
  • AR for finding car
• zipcar
  • book and find cars
  • unlock the car over network, when you’re close to it
• snaptell
  • picture identification
• postage ~ postcards
  • take a picture and send an electronic postcard
  • can apply simple visual effects
  • visually interesting error messages (look like envelopes with postmarks)
• timetuner
  • bedside radio
  • location aware — will take timezone into account
  • can set up custom alerts — different radio stations on different days
  • simple sleep timer on main screen
• weightbot
  • way over the top UI polish…
  • real sounds
  • makes it fun to enter your weight
• tweetie 2
  • only presents UI when you need it
  • swipe down to refresh at top
  • swipe across a tweet to see options
• guitartoolkit
  • swipe across to play strings for a selected chord
  • has tuner
  • has metronome that keeps playing when screen goes dark
  • can do this by setting app type — determines what happens when
• 1112
  • exploration game with lots of extra touches
• ocarina
  • with worldwide
  • and sonic lighter — added messages for choice of flame to mean something
• roambi
  • data interaction with data from SAP, Salesforce etc.
  • lots of visual interaction with data
  • pull through folders, seeing preview of front one
  • pie chart can swivel round to see details of the one on the bottom
  • charts can
• things
  • auto synchronized when iPhone comes into same WiFi network
• MLB.com At Bat
• Flick Fishing
  • using GameKit to hook up to other iPhones
• myStarbucks
  • can send your standard order to someone else so they can order for you
  • (not currently available in UK store)
• ramp champ
  • in-app purchases
  • shows preview, details and price
  • very good catalogue implementation
• iceberg reader
  • iTunes puts up a confirmation dialog of purchase as well
  • shows progress of download in-app
  • (again, not yet available in the UK store — though individual books are)

Apple iPhone Tech Talk London 2009: Networking: From Sockets to GameKit

Paul Danbold danbold@apple.com — Evangelist

This was another really fast presentation with loads of detail. I look forward to grabbing the presentation from the iPhone dev site.

• don’t want to use CFSocket or BSD Socket
  • don’t let you bring up wireless, or involve security
• service discovery:
  • NSNetServices, CFNetServices, dns-sd, BSD Sockets
  • dns-sd is Bonjour or Zeroconf

URL Loading system

• NSURLRequest, NSURLConnection & about 10 other classes (also mutable ones)
• there’s sample code for validating URLs
• recommend to use asynchronous API style:
  • use delegate mechanism — calls connection:didReceiveResponse:
• also connection:didReceiveAuthenticationChallenge:
• finally connectionDidFinishLoading:
• default behaviours should work fine

Local area networking — service discovery

• kick off NSNetServiceBrowser in asynchronous mode, w/delegation
• browser searchForServicesOfType:inDomain:
  • e.g. type _http._tcp in domain local. — don’t go beyond any routers
  • can look for your own types too such as _foo._tcp
• then get myServiceBrowser:didFindService:moreComing:
• call NSNetworkService getInputStream:outputStream to resolve
  • this takes time (many seconds)
  • wait for the user to choose before resolving
  • and let the user decide when to cancel
  • resolveWithTimeout:0.0
• must release input & output stream objects returned by NSNetService
  • bug in Apple’s code — doesn’t obey normal Cocoa behaviour

OutputStream & InputStream

• NSStreamEventHasSpaceAvailable is probably the interesting one
• though you want to handle the errors too…

advertising & publishing

• advertise service with NSNetService initWithDomain:type:name:port
  • domain can be empty — means local
  • name can be blank too — will use device’s iTunes name
• then call publish on service

stop when you’re done

• browsing is fairly lightweight on the network, but you should stop anyway
• the same goes for publishing, when you’ve got all your connected clients

register types & ports

• to register a service type:
  • http://www.dns-sd.org/ServiceTypes.html
  • send them an email, no money changes hands
  • and http://www.iana.org/assignments/port-numbers for one further

game kit — peer to peer

• 3.1 adds WiFi support as well as Bluetooth
• GKSession initWithSessionID:displayName:sessionMode
  • session ID is your Bonjour service type — how you advertise yourself
  • again, can leave displayName as nil for iTunes name
  • sessionMode can be peer to peer (1 to 1) or client/server (multiple clients)
• can’t physically go over 10-20 clients with Bluetooth
  • 3.1 and later is a lot better, but still no more than 3-4 clients
  • Bluetooth also has low bandwidth
• set up delegate and set available to YES
• check other peers with peersWithConnectionState:
  • can be available, already connected, in the process of getting connected
• connectToPeer:withTimeout:
  • generally set timeout to zero to let user cancel if they want
• actual connection made with session:didReceiveConnectionRequestFromPeer: and acceptConnectionFromPeer:error:
• must monitor the network using session:peer:didChangeState:
  • other players can drop out, so you’d have to tear down your session
• send data with sendDataToAllPeers:withDataMode:error: and sendDataToPeers:...
  • can choose unreliable (UDP) or reliable (TCP) data modes
  • as always TCP imposes a performance cost so use sparingly
• receive data with setDataReceiveHandler:withContext: and receiveData:fromPeer:inSession:context:
• always check for errors — buffers fill up on low bandwidth networks
  • check it by using a slow network
• when you’re finished, tear down with disconnectFromAllPeers:
• there’s a GKPeerPickerController for setting up Bluetooth peers
  • doesn’t work for client/server or WiFi
• the only way to find out if Bluetooth is turned on is to use the GKPeerPickerController (it uses private APIs…)
• all data sent & received is NSData-wrapped — design your packaging for network efficiency first and coding efficiency second

Voice chat

• GKVoiceChatClient and ~Service
• sets up socket interface
• handles microphone, echo suppression, etc

network challenges

scoped routing and reachability

• iphone 3.0 and later provides scoped routing
  • keeps both cellular and wifi up at the same time — so cellular connections keep going when you enter a wifi hotspot
  • but this puts a toll on the battery, so you should behave and check for networking changes
• use SystemConfiguration APIs to monitor network state
  • Am I on the network and what kind of network is it?
  • cannot tell you that packets will arrive…
  • if network changes, finish what you’re doing, close connection and start a new one
• use SCNetworkReachabilityRef and check for flags
  • but again use callback APIs since the calls take about 30 seconds
• no point using this to pre-flight as things may change
  • just use to monitor
• can set UIRequiresPersistentWiFi key
  • keeps WiFi live while your app is live
  • shows up UI elements automatically (like offering to turn off Airplane mode)
  • but if the device sleeps, you still lose your WiFi connection

battery use

• listening is cheap, transmitting is expensive
• 3GS sending leaves the antenna in high powered state for 5 seconds
  • so don’t send every 5 seconds — it will leave it in high power continuously
• compress data, send large chunks
• tear down connections when reachability changes

other tips

• try to use the cache as much as possible
• try to resume downloads rather than restart
• use pipelining if poss.
  • ask for lots of things at once and be careful about return order
  • some web proxies and apache configs just break pipelining
• also use multiple connections
• but different network conditions and different servers require different tuning
• test in areas where you know the network is flaky!
• use a packet analyzer — see QA1176
• try to isolate the user from network problems
  • often there’s a transient glitch — try again before alerting the user
• see also Technote TN2152
• look for developer forum postings by eskimo1 :-)

there’s some new sample code available:

• SimpleNetworkStreams
• SimpleURLConnection
• SimpleFTPSample
• Reachability — there’s a new version! The old version had bad code :-)
• BonjourWeb
• WiTap — peer to peer, but doesn’t use GameKit
• GKTank
• GKRocket — work in progress, with voice chat too

Apple iPhone Tech Talk London 2009: Testing and Debugging Your iPhone Application

Just before this session, I had an interesting discussion with Mike Llewellyn, author of Broadersheet, about unit testing. He uses defensive code with asserts and logging and doesn't think there is enough value in unit testing for mostly UI code.

However, Apple have converted to using unit tests and are making it easy for XCode developers to take advantage of them.

At Kizoom, we’ve used unit tests to test our controller code — ensuring that given a particular input, it goes to the right result view with the appropriate model. This is made easier by using three20 — the result view is identified by a string rather than an object (though using OCMock would let you assert about objects too).

Here’s what Michael Jurewitz jurewitz@apple.com — App Frameworks & Dev Tools Evangelist had to say:

• thousands of tests in Core Data
  • roughly 90% coverage (that’s very impressive — it’s hard to maintain more than 80%)
  • fully test driven from the start
• similarly large amount of tests in WebKit
• Application tests get injected into application and can drive running app

static analysis

• has found and fixed thousands of bugs in Snow Leopard & iPhone OS :-)
• use it to learn and enforce good Cocoa practices
• detects dead stores: unused variables
• see “Run Static Analyzer” in Project properties / Build
  • might not want to have this for all configurations
  • gets picked up by xcodebuild on the command line

organizer

• check the console if you get a crash
• can download app’s data from actual device:
  • check Applications under Summary — your app will have a disclosure arrow

beta testing

• create a distribution certificate in the iPhone portal
• create an adhoc provisioning profile
  • can still use a wildcard identifier
• load it up into XCode
• make a beta testing config
  • duplicate the release config
  • set Code Signing Entitlements to Entitlements.plist (a new file)
  • use appropriate provisioning profile
  • create new Entitlements: set get-task-allow to false
  • disallows debugging
  • if you want people to debug, then send them a debug build…
• build + send zip of build + provisioning profile to beta testers
• they can unzip & drag both to iTunes

crashes

• can get crash log from user — iTunes syncs them
  • Mac & Windows store them in different places, but can find…
  • also available in iTunes Connect
• can get Organizer to symbolicate crash log for you
  • your .app and .dSym must be locatable by Spotlight — so keep them

low memory logs

• see count of pages: each page is 4Kb
• SpringBoard shares memory with your app — it handles presentation on screen
• mediaserverd is iPod
• if you find that something other than your app or SpringBoard is the largest memory user, then file a bug…

other crashes

EXC_CRASH (SIGABRT)

• 0xdeadfa11 — termination due to too much memory
• 0x8badf00d — watchdog timeout

EXC_BAD_ACCESS (SIGBUS)

• objc_msgSend — happens when you message a deallocated object

instruments

• Zombies template — record reference counts & enabled NSZombie detection
  • see extended detail view using rectangle icon at bottom of window
  • shows stack trace for each event
  • can jump through to code view, then jump into XCode editor